Hi, I tried your game and must admit it was tricky to get it to work. Some of these things might be related with me using gosu 1.9 and not 2.0 as recommended, but you might want to double check it.
First of all, I had to convert all mp3's to ogg (gosu likes to be fussy about this). Then I got NilClass error in Particle class (line 68), fixed it by adding
at the end but I don't really think it's the right solution.
The game started, but there's still another problem - most texts don't fit on the screen (screenshots
Other than that, it's a cool idea that looks good and plays good. I love the particle effects!